1. Field of the Invention
The present invention relates to two-dimensional optical filters and methods, and, more particularly, to such devices and methods having high spectral resolution and being adapted for continuous tuning.
2. Description of Related Art
The spectral filtering of multicolor images has been studied [1], resulting in filters employing absorption [2-7], dispersion [7-11], selective reflection [12-15], and spectrally selective transmission [1, 16-22]. A variety of techniques are known for spectral image filtering [23], including dichroic coated filters [24-27], holographic filters [28-35], acousto-optic tunable filters [35], Fabry-Perot tunable filters [24, 35-39], tunable birefringent filters [23, 40-46], and Lyot filters [23, 43-47]. The filtration mechanisms vary from the use of Bragg diffraction caused by periodically modulated refractive indices in holographic and acousto-optic tunable filters to the use of selectivity in transmission by polarization in Lyot filters. The basic underlying objective is the selective transmission, absorption, or reflection of a selected optical range. These techniques and their development for enhancing tunability and spectral sensitivity have been ongoing for some time [50-52].
High-sensitivity charge-coupled-device (CCD) cameras can be combined with notch filters for high-spectral-resolution two-dimensional imaging or with bandpass filters for broadband imaging. However, the dual requirements of fidelity of two-dimensional spatial imaging and high-resolution, continuous spectral tunability are not known to be available in currently existing systems.
It is therefore an object of the present invention to provide an optical filter adapted to separate a multifrequency, two-dimensional image into spectral components.
It is an additional object to provide such a filter that retains the integrity of the two-dimensional image.
It is a further object to provide a method for making such a filter.
It is another object to provide a method for using such a filter.
These objects and others are attained by the present invention, an optical filter system for separating an image into spectral components. The filter comprises a plurality of input optical fibers, each having a first end and a second end. The first ends are two-dimensionally arrayed and are thus substantially coplanar; the second ends are substantially linearly arrayed and are thus also substantially coplanar. Each input fiber is configured to receive a portion of a two-dimensional input image at the first end and transmit the image portion to the second end.
A spectrally dispersive element following the input fiber array is configured to receive the image portions from the input fiber second ends and to output separated spectral components thereof.
A plurality of output optical fibers each has a first end and a second end. The first ends are substantially linearly arrayed and thus are substantially coplanar; the second ends are two-dimensionally arrayed and are also thus substantially coplanar. Each output fiber is configured to receive a portion of the output of the spectrally dispersive element at the first end and transmit the image portion to the second end. Further, the second ends are arrayed in corresponding fashion to the first ends of the input fibers for spatially reconstructing the input image.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.